This invention relates to semiconductor materials. More particularly, it is concerned with methods of introducing conductivity type imparting material into III-V compound semiconductor materials.
It has been difficult to diffuse donor materials, which impart N-type conductivity, into III-V compound semiconductor materials, specifically gallium arsenide. At the high temperatures required to diffuse donor material into gallium arsenide there is a preferential arsenic evaporation from the gallium arsenide resulting in heavily eroded surfaces. Therefore, it has been the practice to introduce donor materials, particularly silicon, into III-V compound semiconductor materials by ion implantation techniques to produce N-type material.
Ion implantation techniques cause crystalline damage which must be annealed out by a high temperature treatment, carefully controlled so as not to cause degradation of the surface. The peak concentration of ion implanted materials is located below the surface. This carrier concentration profile results in metal-semiconductor field effect transistors (MESFETs) having low transconductance. For high transconductance devices very shallow, highly-doped N-type surface layers are desired in which the carrier concentration is at a maximum at the surface dropping very rapidly into the bulk of the material.
One procedure for obtaining a satisfactory N-type diffusion profile in gallium arsenide employs a sealed ampule technique. A gallium arsenide wafer is vacuum sealed in a quartz ampule together with the donor source and arsenic, and heated in a furnace at a temperature of between 800.degree. C. to 900.degree. C. After diffusion the ampule is withdrawn from the furnace and the source side of the ampule quenched to prevent deposition of vapor on the wafer surface during cooling. This method, however, is very limited and is not suitable for large-scale production of gallium arsenide integrated circuits.